The measurement of displacement of movable equipment, such as a sucker rod, at the surface and the force or stress to which this rod is subjected are currently made and serve for the construction of a stroke-force diagram. The diagram of Leuter, is described, for example, in U.S. Pat. No. 4,583,915 Montgomery et al. The programs of calculation permit transposing the diagram construction by the use of values measured on the rod outside the well at the surface, which deviate considerably from those in the well, particularly on the bottom rod located immediately above the pump. It is this action of behavior of a lower rod which must be know to optimize pumping parameters. On different occasions, particularly where verification of position has been possible, or after rupture of the rod, it is apparent that transposing surface data to the portions moving in the well present many risks.
The measurement of the forces or stresses of the sucker rod at the bottom of the well is a known technique, and the transmission to the surface of the measurements made at the bottom can be done by a wire, by an acoustic system using the annular mud as the medium of propagation, or even storing the measurement data at the bottom in volatile memory (in english, Random Access Memory or R.A.M.) which is exploited after pulling the string of sucker rods.
Measurements of the displacement of the rod at the bottom of the well have been obtained in an experimental well by using a specially made section of production pipe and a proximity detector. The indications obtained are fed to the surface by a cable.
The use of a pipe, such as a production pipe, having markings on its internal wall constitutes a constraint which it is necessary to eliminate in order to make this technique workable. Such is the object of the present invention which has reduced the use of control equipment and pulling of the sucker rods or other movable equipment from the well.